Ethylene-vinyl acetate (EVA) copolymers are random copolymers of ethylene and vinyl acetate. They are widely used as cable insulating compositions, as hot-melts, or in the form of sheets.
One outstanding characteristic is their good thermal stability. Fabricating temperatures up to 240.degree. C are used for many EVA copolymers without resulting in decomposition.
The evolving of acetic acid, from sheet materials for example, would be highly undesirable, since it would result in damage to the packaging and to the goods packed.
On the other hand, a controlled partial or complete splitting off of acetic acid from the unfabricated polymeric raw material with the formation of carbon-to-carbon double bonds would be very attractive because this would make available novel, unsaturated EVA copolymers or unsaturated polyethylenes which might be starting products for a series of new products or syntheses. The splitting off can also be used for analytic analysis. See infra.
In this specification the term "deacetylation" will be used to refer to the cleavage of acetic acid from the vinyl acetate building block or group ##STR1## of the EVA copolymers with the formation of a double bond issuing from the C.sub.1 atom, without the occurrence of secondary reactions such as oxidation, cross-linking, absorption of an acid ester or other atoms or atom groups, molecular cleavage, or conversion of the macromolecule. In the formula, AZ is an acetate group.
The cleavage of acetic acid from EVA copolymers for the purpose of the analytic detection of the vinyl acetate polymerized into EVA copolymers is known. For example, a pyrolytic cleavage of acetic acid from EVA copolymers for the analytic detection of the bound vinyl acetate has been described by D. Braun in "Mitteilungen aus dem Deutschen Kunststoff-Institut," Darmstadt, No. 12, page 3 (1972). In this process decomposed residues and highly crosslinked residues are produced.
R. C. Schulz and collaborators describe a method of analysis for the quantitative determination of vinyl acetate in EVA copolymers through the treatment of these copolymers with an approximately 30-fold excess of molten toluenesulfonic acid at 160.degree. C ("Die Angewandte Makromolekulare Chemie" 24 (1972) 171-175). In this case, too, the greatly discolored residues are unusable.